Numerous optical systems exist that are used for detecting the position of a member or an article in order to input data, and in particular alphanumeric data.
French patent FR 2 443 173 describes a keyboard having moving keys and a plurality of light sources and light sensors enabling key depressions to be detected; that keyboard is expensive since it requires large numbers of mechanical components and of optoelectronic components; it is also complex because of the way the light sources and sensors are spread throughout the zone in which the keys are situated.
More recently, static devices (having no moving keys) have been developed for inputting data.
Document GB-A-2 133 537 describes a system for optically detecting the position of a user's finger on a screen; that system comprises sources emitting diverging light beams in order to increase the resolution of the system without multiplying the number of emitters and detectors.
U.S. Pat. No. 4,986,662 describes a system similar to the preceding system in which the sources are placed at the focal point of a parabolic reflector in order to decrease the number of optoelectronic components.
A drawback of those devices results from the fact that they require optical components (sources, detectors, and where necessary reflectors) to be placed in substantially distributed manner around the perimeter of the input zone (or monitored zone), and for this to be done with sufficient geometrical accuracy to avoid falsifying the calculations performed on the basis of data representative of the signals delivered by the detectors in order to determine the position in the input zone of an obstacle (finger, etc.) serving to define the data selected by the user. As a result, those devices remain relatively expensive.
Document EP 0 559 357 describes an alarm system including a “photoelectric barrier” type detector device constituted by two posts standing on the ground and fitted with four emitters producing four superposed infrared beams, and corresponding receivers which detect when the beams are interrupted by articles passing through the infrared barrier. The system for processing the binary signals delivered by the detectors comprises in succession: a multiplexer; a graphics generator representing interruptions of the infrared beams by the passage of a man, an animal, or an article; a preprocessor; a neural network; a comparator; a controller connected to an alarm; and a display and/or printer device. After a period of training, the neural network can be used to recognize by comparison the type of an article from among a predetermined set of article types (man, animal, vehicle), as a function of the graphics representation generated from the signals detecting interruptions of the superposed infrared beams.
That system is not designed to determine the position of an article in the monitored zone; nor is it suitable for so doing since neither the emitters nor the detectors cover the entire zone that is to be monitored.
Document EP 0 506 039 describes a device for detecting the position of the cutting edge 8a, 8b of a cutter tool 8 relative to a V-notch in a plate.
For this purpose, the device comprises a laser source directed towards the V-slot separating the cutting edge from the edge of the reference plate, an optical system responsive to the fringes that result from the laser beam being diffracted by the slot, and a neural network for determining the position of the cutting edge on the basis of signals delivered by the optical system; the optical system comprises either three series of photodiodes in alignment, or else a CCD camera.
The use of diffraction fringes from a laser beam is not applicable to detecting the position of a finger in a zone of determined outline insofar as the presence of a finger does not lead to the presence of diffraction fringes.